Sleeve molding

ABSTRACT

Sleeve molding apparatus and methods for making multi-layer injection molded plastic articles in successive mold cavities. In a first molding step, an inner sleeve is molded on a core in a first mold cavity, which may comprise a full body length sleeve or only a partial sleeve, such as an upper neck finish portion. The sleeve and core are withdrawn from the first mold cavity while the sleeve is still warm, and transferred without substantial delay to a second mold cavity for injection molding an outer layer which bonds to the inner sleeve. By transferring the sleeve at an elevated temperature into the second mold cavity, an improved bond is formed between the inner sleeve and outer layer which resists separation during a later reheat stretch blow molding step, and/or in use of the resulting article. In a preferred embodiment, a pasteurizable beer container is provided having a finish-only sleeve of a PEN polymer. In a second embodiment, a returnable and refillable water container is provided having a full-length body sleeve of a PEN polymer. A multi-station injection molding apparatus is provided having a transfer mechanism, such as a rotatable turret or reciprocating shuttle, for cost-effective manufacture of preforms simultaneously in multiple cavity sets.

RELATED APPLICATIONS

This is a Continuation Application under 37 C.F.R. §1 53(b) of priorapplication Ser. No. 08/981,467 filed Mar. 17, 1998 now U.S. Pat. No.6,428,737 of Wayne N. Collette and Suppayan M. Krishnakumar for SLEEVEMOLDING, which is a continuation of PCT/US96/11413 filed Jul. 8, 1996,and a continuation-in-part of U.S. Ser. No. 08/534,126 filed Sep. 26,1995 (now U.S. Pat. No. 6,217,818 dated Apr. 17, 2001), which is acontinuation-in-part of U.S. Ser. No. 08/499,570 filed Jul. 7, 1995 (nowabandoned), all of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for makingmultilayer injection-molded plastic articles such as preforms, whereinthe successive molding of an inner sleeve and outer layer enablescost-effective production of multilayer preforms for pasteurizable,hot-fillable, and returnable and refillable beverage containers.

BACKGROUND OF THE INVENTION

There is described in U.S. Pat. No. 4,609,516 to Krishnakumar et al. amethod for forming multilayer preforms in a single injection moldcavity. In that method, successive injections of different thermoplasticmaterials are made into the bottom of the mold cavity. The materialsflow upwardly to fill the cavity and form for example a five-layerstructure across the sidewall. This five-layer structure can be madewith either two materials (i.e., the first and third injected materialsare the same) or three materials (i.e., the first and third injectedmaterials are different). Both structures are in widespread commercialuse for beverage and other food containers.

An example of a two-material, five-layer (2M, 5L) structure has inner,outer and core layers of virgin polyethylene terephthalate (PET), andintermediate barrier layers of ethylene vinyl alcohol (EVOH). An exampleof a three-material, five-layer (3M, 5L) structure has inner and outerlayers of virgin PET, intermediate barrier layers of EVOH, and a corelayer of recycled or post-consumer polyethylene terephthalate (PC-PET).Two reasons for the commercial success of these containers are that: (1)the amount of relatively expensive barrier material (e.g., EVOH) can beminimized by providing very thin intermediate layers; and (2) thecontainer resists delamination of the layers without the use ofadhesives to bond the dissimilar materials. Also, by utilizing PC-PET inthe core layer, the cost of each container can be reduced without asignificant change in performance.

Although the above five-layer, and other three-layer (see for exampleU.S. Pat. No. 4,923,723) structures work well for a variety ofcontainers, as additional high-performance and expensive materialsbecome available there is an on-going need for processes which enableclose control over the amount of materials used in a given containerstructure. For example, polyethylene naphthalate (PEN) is a desirablepolyester for use in blow-molded containers. PEN has an oxygen barriercapability about five times that of PET, and a higher heat stabilitytemperature—about 250° F. (120° C.) for PEN, compared to about 175° F.(80° C.) for PET. These properties make PEN useful for the storage ofoxygen-sensitive products (e.g., food, cosmetics, and pharmaceuticals),and/or for use in containers subject to high temperatures (e.g., refillor hot-fill containers). However, PEN is substantially more expensivethan PET and has different processing requirements: Thus, at present thecommercial use of PEN is limited.

Another high-temperature application is pasteurization—a pasteurizablecontainer is filled and sealed at room temperature, and then exposed toan elevated temperature bath for about ten minutes or longer. Thepasteurization process initially imposes high temperatures and positiveinternal pressures, followed by a cooling process which creates a vacuumin the container. Throughout these procedures, the sealed container mustresist deformation so as to remain acceptable in appearance, within adesignated volume tolerance, and without leakage. In particular, thethreaded neck finish must resist deformation which would prevent acomplete seal.

A number of methods have been proposed for strengthening the neckfinish. One approach is to add an additional manufacturing step wherebythe neck finish, of the preform or container, is exposed to a heatingelement and thermally crystallized. However, this creates severalproblems. During crystallization, the polymer density increases, whichproduces a volume decrease; therefore, in order to obtain a desired neckfinish dimension, the as-molded dimension must be larger than the final(crystallized) dimension. It is thus difficult to achieve closedimensional tolerances and, in general, the variability of the criticalneck finish dimensions after crystallization are approximately twicethat prior to crystallization. Another detriment is the increased costof the additional processing step, as it requires both time and theapplication of energy (heat). The cost of producing a container is veryimportant because of competitive pressures and is tightly controlled.

An alternative method of strengthening the neck finish is to crystallizeselect portions thereof, such as the top sealing surface and flange.Again, this requires an additional heating step. Another alternative isto use a high T_(g) material in one or more layers of the neck finish.This also involves more complex injection molding procedures andapparatus.

Thus, it would be desirable to provide an injection-molded article suchas a preform which incorporates certain high-performance materials, anda commercially acceptable method of manufacturing the same.

SUMMARY OF THE INVENTION

The present invention is directed to a method and apparatus for making amultilayer injection-molded plastic article, such as a preform, which isboth cost-effective and enables control over the amounts of materialsused in the various layers and/or portions of the article.

According to a method/embodiment of the invention, an inner sleeve ismolded on a first core positioned in a first mold cavity. The innersleeve is only partially cooled before being transferred while still atan elevated temperature to a second mold cavity where an outer layer ismolded over the inner sleeve. By providing the inner sleeve in thesecond mold cavity at the elevated temperature, bonding between theinner sleeve and outer layer is enabled during the second molding step,such that layer separation is avoided in the final molded article. Theinner sleeve may comprise a full-length inner sleeve, extendingsubstantially the full length of the article, or alternatively maycomprise only an upper portion of the article, in which case the outerlayer comprises a lower portion of the article and there is someintermediate portion in which the outer layer is bonded to the innersleeve.

In one embodiment, a first thermoplastic material is used to make aninner sleeve which comprises a neck finish portion of the preform. Thefirst thermoplastic material is preferably a thermal resistant materialhaving a relatively high T_(g), and/or forms a crystallized neck finishduring the first molding step. In contrast, a lower body portion of thepreform is made of a second thermoplastic material having a relativelylower thermal resistance and/or lower crystallization rate compared tothe first material, and forms a substantially amorphous body-formingportion of the preform. In one example, by achieving crystallization inthe neck finish during the first molding step, the initial and finishdimensions are the same so that the dimensional variations caused by theprior art post-molding crystallization step (and the expense thereof)are eliminated. Also, a higher average level of crystallization can beachieved in the finish, by utilizing the higher melt temperatures and/orelevated pressures of the molding process.

In another embodiment, a full-length body sleeve is provided made of ahigh-performance thermoplastic resin, such as PEN homopolymer, copolymeror blend. The PEN inner sleeve provides enhanced thermal stability andreduced flavor absorption, both of which are useful in refillapplications. The amount of PEN used is minimized by this process whichenables production of a very thin inner sleeve layer, compared to arelatively thick outer layer (made of one or more lower-performanceresins).

Another aspect of the invention is an apparatus for the cost-effectivemanufacture of such preforms. The apparatus includes at least one set offirst and second molding cavities, the first mold cavity being adaptedto form the inner sleeve and the second mold cavity adapted to form theouter layer. A transfer mechanism includes at least one set of first andsecond cores, wherein the cores are successively positionable in thefirst and second molding cavities. In one cycle, a first core ispositioned in a first mold cavity while a first inner sleeve is moldedon the first core, while a second core, carrying a previously-moldedsecond inner sleeve, is positioned in a second mold cavity, for moldinga second outer layer over the second inner sleeve. By simultaneouslymolding in two sets of cavities, an efficient process is provided. Bymolding different portions/layers of the articles separately indifferent cavities, different temperatures and/or pressures may be usedto obtain different molding conditions and thus different properties inthe different portions/layers. For example, it is possible to mold thecrystallized neck finish portion in a first cavity, while molding asubstantially amorphous outer layer in the second cavity.

The resulting injection-molded articles, and/or expandedinjection-molded articles, may thus have a layer structure which is notobtainable with prior processes.

The following chart provides temperature/time/pressure ranges forcertain preferred embodiments, which are described in greater detail inthe following sections:

a) for an inner sleeve of PEN polymer material and an outer layer of PETpolymer material

range (on the order of) first molding step: core temperature  5-80° C.mold cavity temperature 40-120° C. melt temperature 275-310° C.  cycletime 4-8 seconds outer surface temperature of sleeve 60-120° C. secondmolding step: core temperature  5-80° C. mold cavity temperature  5-60°C. cycle time 20-50 seconds pressure 8000-15,000 psi

b) for an inner sleeve of crystallized polyester material and an outerlayer of PET polymer material

range (on the order of) first molding step: core temperature  5-60° C.mold cavity temperature 80-150° C. melt temperature 270-310° C.  cycletime 5-8 seconds outer surface temperature of sleeve 80-140° C. secondmolding step: core temperature  5-60° C. mold cavity temperature  5-60°C. cycle time 20-35 seconds pressure 8000-15,000 psi

The present invention will: be more particularly set forth in thefollowing detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D are schematic illustrations of a first method embodiment ofthe present invention for making a preform having a full-length innersleeve and a single outer layer;

FIGS. 2A-2B are schematic illustrations of an injection-moldingapparatus and the sequence of operations for making a preform such asthat shown in FIG. 1D, wherein a rotary turret transfers two sets ofcores between two sets of cavities; FIG. 2A shows the cavities/cores ina closed position and FIG. 2B shows the cavities/cores in an openposition;

FIG. 3 is a time line showing the sequence of operations for the moldingapparatus of FIG. 2;

FIG. 4A is a front elevational view of a returnable and refillablecontainer, partially in section, made from the preform of FIG. 1D, andFIG. 4B is an enlarged fragmentary cross-section of the containersidewall taken along the line 4B—4B of FIG. 4A;

FIGS. 5A-5D are schematic illustrations of a second method embodiment ofthe present invention for making a preform having a finish only sleeveand a multilayer outer layer;

FIGS. 6A-6D are schematic illustrations of an injection-moldingapparatus and sequence of operations for making a preform such as thatshown in FIG. 5D, wherein the transfer mechanism is a reciprocatingshuttle; FIG. 6A shows the shuttle in a first closed position in firstand second mold cavities; FIG. 6B shows the shuttle in a second openposition after retraction from the first and second mold cavities; FIG.6C shows the shuttle in a second open position beneath the second andthird mold cavities; and FIG. 6D shows the shuttle in a fourth closedposition in the second and third mold cavities;

FIG. 7 is a time line of the sequence of operations shown in FIG. 6;

FIG. 8A is a cross-sectional view of a third preform embodiment of thepresent invention having a full-thickness neck sleeve and multilayerbody portion, and FIG. 8B is an enlarged fragmentary view of the neckfinish of the preform of FIG. 8A;

FIG. 9A is a front elevational view of a hot-fill container made fromthe preform of FIG. 8A, and FIG. 9B is a fragmentary cross-section ofthe container sidewall taken along line 9B—9B of FIG. 9A;

FIG. 10 is a cross-sectional view of a fourth preform embodiment of thepresent invention, having a full-length body sleeve and multilayer outerlayer;

FIG. 11 is a cross-sectional view of a fifth preform embodiment of thepresent invention, including a full-length body sleeve and an extraouter base layer;

FIG. 12 is a cross-sectional view of a sixth preform embodiment of thepresent invention, having a finish sleeve and a single layer outerlayer;

FIGS. 13A and 13B are graphs showing the change in melting temperature(MP) and orientation temperature (T_(g)) for various PEN/PETcompositions; and

FIG. 14 is a schematic illustration of a three-station reheatingapparatus, including IR heating stations A and C and RF heating stationB.

DETAILED DESCRIPTION

First Preform Embodiment (Refillable Water)

FIGS. 1A-1D illustrate schematically one method embodiment for making apreform with a full-length body sleeve and a single outer layer; thispreform is particularly useful for making a returnable and refillablewater bottle. FIG. 1A shows a first core 9 positioned in a first moldcavity 11, and forming a chamber therebetween in which there is formedan injection-molded inner sleeve 20. The sleeve 20 is partially cooledand then the core 9 carrying sleeve 20 is removed from the first moldcavity as shown in FIG. 1B. While still warm, the sleeve 20 on core 9 isinserted into a second mold cavity 12 which forms an interior moldingchamber for forming an outer layer 22 over the inner sleeve 20. Afterthe second molding step, a preform 30 has been formed including outerlayer 22 and inner sleeve 20 as shown in FIG. 1D. The inner sleeveincludes a top flange 21 which will form the top sealing surface of theresulting container (see FIG. 4).

The first method embodiment will now be described in greater detail inregard to the apparatus shown in FIGS. 2A-2B, and a time sequence ofoperations illustrated in the time line of FIG. 3.

As shown in FIGS. 2A-2B, a four-sided rotatable turret 2 is interposedbetween a fixed platen 3 and a movable platen 4 on an injection-moldingmachine. The turret 2 is mounted on a carriage 5 which is slidable inthe direction of platen motion (shown by arrows A₁ and A₂). The turret 2is rotatable (shown by arrow A₃) about an axis 6 disposed perpendicularto the direction of platen motion. The turret is rotatable into twooperative positions spaced 180° apart. In each of these positions, thetwo opposing faces 7, 8 of the turret carrying first and second sets ofcores 9, 10 respectively, are received in a first set of cavities 11 onthe movable platen 4, and a second set of cavities 12 on the fixedplaten 3. After a core set has been successfully positioned in each ofthe mold cavities, the finished preforms may be ejected from the cores.Each of the mold cavity and core sets include water passages 15 forheating or cooling of the cavities/cores to achieve a desiredtemperature during molding.

The sequence of operations for forming a particular preform will now bedescribed. The preform has a full-body sleeve of a PEN polymer, such ashomopolymer PEN, or a PEN/PET copolymer or blend. The preform has asingle outer layer made of virgin PET.

In FIG. 2A, the movable platen 4 carrying the first set of mold cavities11, and the carriage 5 carrying the turret 2, are each moved on guidebars (tie rods) 13, 14 to the left towards the fixed platen 3 to closethe mold (i.e., both cavities). The first set of cores 9 on the leftface 7 of the turret are positioned in the first cavity set 11 (firstmolding station); each first core/cavity pair defines an enclosedchamber for molding an inner sleeve about the first core. The PENpolymer is injected via nozzle 16 into the first mold cavities to formthe inner sleeve. Simultaneously, the second core set 10 (on the secondface 8 of the turret) is positioned in the second cavity set 12 (secondmolding station). Virgin PET is injected via nozzle 17 into the secondset of cavities to form a single outer layer about a previously-formedinner sleeve on each of the second cores.

Next, the mold is opened as shown in FIG. 2B by moving both the movableplaten 4 and carriage 5 to the left, whereby the first cores 9 areremoved from the first cavity 11 and the second cores 10 are removedfrom the second cavity 12. Now, the finished preforms 30 on the secondcore set are ejected. The finished preforms 30 may be ejected into a setof robot cooling tubes (not shown) as is well known in the art. Next,the turret 2 is rotated 180°, whereby the first set of cores 9 with theinner sleeves 20 thereon are now on the right side of the turret (andready for insertion into the second set of cavities), while the secondset of (empty) cores 10 is now on the left side of the turret (ready forinsertion into the first set of mold cavities). Again, the mold isclosed as shown in FIG. 2A and injection of the polymer materials intothe first and second sets of cavities proceeds as previously described.

In this embodiment, the first and second cores are held at a temperaturein a range on the order of 60-70° C., whether they are positioned in thefirst mold cavities or the second mold cavities. The first mold cavities(for forming the inner sleeve) are held at a temperature on the order of85-95° C. The melt temperature of the PEN polymer is on the order of285-295° C. The cycle time in the first mold cavity is on the order of6-7 seconds, i.e., the time lapse between the first and secondinjections. This is because, as shown in FIG. 3, the hold and cool stageis substantially eliminated in the first mold cavities. The outersurface temperature of the sleeve (opposite the inner surface engagingthe core) at the start of the second injection is 100-110° C.

During the second molding step, the core temperature is again at 60-70°C., but the second mold cavity temperature is 5-10° C. (much lower thanthe first cavity temperature, to enable quick cooling of the preform).The melt temperature of the virgin PET is on the order of 260 to 275°C.; this is lower than the melt temperature of the PEN polymer, butbecause the PEN polymer is still warm (at a temperature of 100-110° C.)during the second molding step, there is melt adhesion (includingdiffusion bonding and chain entanglement) which occurs between the PENpolymer chains and virgin PET polymer chains (inner sleeve and outerlayer) respectively. The cycle time for the second molding step is onthe order of 35 to 37 seconds.

FIG. 3 is a time line with the cycle time along the x axis (time inseconds), and the sequence of steps in the second cavity set shown abovethe x axis, and the sequence of steps in the first cavity set shownbelow the x axis. At t=0, the mold is closed (see FIG. 2A) and thepressure is built up. At t=1.5 seconds, the second cavity (for formingthe outer layer) is filled, the pressure boosted, and then the pressurereduced during the hold and cooling stage; this continues until t=33seconds in the second cavity. Meanwhile, no action is required at t=1.5seconds in the first cavity (“no action period”); rather, it is notuntil t=31 seconds that the first cavity is filled and the pressureincreased and held, until t=33 seconds. This substantial elimination ofthe hold and cooling stage (in the first cavity) produces an innersleeve which is still at an elevated temperature when it is subsequentlyis positioned in the second cavity, and enables melt adhesion betweenthe outer surface of the inner sleeve and outer layer. At t=33 seconds,the mold is opened (see FIG. 2B), and the preforms from the secondcavity are ejected. Then, at t=35 seconds, the turret 2 is rotated so asto position the still-warm sleeves (just made in the first cavity) in aposition to be inserted into the second cavity, while the now-empty coreset (previously in the second cavity) is now positioned to be insertedin the first cavity. At t=36 seconds, we are ready to begin the nextcycle.

The method and apparatus of FIG. 2 may be advantageously used to producemultilayer preforms for a great variety of applications, includingrefill, hot-fill and pasteurizable containers. A number of alternativeembodiments are described below.

The preform made according to the method and apparatus of FIGS. 1-3includes a full-body inner sleeve 20 of PEN polymer, and a single outerlayer 22 of virgin PET. The preform is substantially transparent andamorphous and may be reheated and stretch blow-molded to form a 1.5liter returnable and refillable water bottle, such as that shown in FIG.4A. The container 40 is about 13.2 inches (335 mm) in height and about3.6 inches (92 mm) in widest diameter. The container body has an opentop end with a small diameter neck finish 42 having external screwthreads for receiving a screw cap (not shown), and a closed bottom endor base 48. Between the neck finish 42 and base 48 is a substantiallyvertically-disposed sidewall 45 (defined by vertical axis or centerlineCL of the bottle), including a substantially cylindrical panel portion46 and a shoulder portion 44 tapering in diameter from panel 45 to neckfinish 42. The base 48 is a champagne-style base with a central gateportion 51 and, moving radially outwardly towards the sidewall, anoutwardly concave dome 52, an inwardly concave chime 54, and a radiallyincreasing and arcuate outer base portion 56 for a smooth transition tothe sidewall panel 46. The chime 54 is a substantially toroidal-shapedarea around a standing ring (chime) on which the bottle rests.

FIG. 4B shows in cross-section the multilayer panel portion 46, whichincludes an inner sleeve layer 41 (an expanded version of preform sleeve20), and an outer layer 43 (an expanded version of preform outer layer22). One benefit of the present invention is that the layers 41 and 43have bonded and will not separate during reheat stretch blow molding oruse of the container, in this case including the intended 20 or morerefill cycles. In addition, a flange 47 (same as flange 21 of thepreform) forms a top sealing surface of the container with increasedstrength and thermal resistance.

Second Preform Embodiment (Pasteurizable Beer)

FIGS. 5A-5D illustrate schematically a second method embodiment formaking a finish-only sleeve and a multiple outer layer preform; thispreform is adapted for making a pasteurizable beer container. FIG. 5Ashows a core 207 positioned in a first mold cavity 213; together theyform a first molding chamber in which a finish-only sleeve 250 isinjection molded. FIG. 5A shows an injection nozzle 211 in the moldcavity 213, through which a molten thermoplastic material is injectedfor forming the sleeve 250. FIG. 5B shows the formed sleeve 250 on thecore 207, the sleeve having been removed from first mold cavity 213while it is still warm. The core 207 carrying the sleeve 250 is thenpositioned in a second mold cavity 214 as shown in FIG. 5C. The secondmold cavity 214 and core 207 form a second molding chamber adapted toform an outer layer 252 over the inner sleeve 250. A plurality ofdifferent thermoplastic materials are injected through a gate 209 in thebottom of the second mold cavity 214, to form the multiple outer layers.As shown in FIG. 5D, the outer layer 252 extends the full length of thepreform. A sequential injection process such as that described in U.S.Pat. No. 4,609,516 to Krishnakumar et al., may be used to form inner andouter layers 253, 254 of virgin PET, core layer 255 of recycled PET(which may include an oxygen scavenging material), and inner and outerintermediate layers 256, 257 of an oxygen barrier material, between theinner/core/outer layers. In this embodiment, only the virgin PET extendsup into the neck finish of the preform, forming a single layer 258 overinner sleeve 250. In the base of the preform, a final injection ofvirgin PET forms a plug 259 for clearing the nozzle before the nextinjection cycle.

FIGS. 6A-6D illustrate a reciprocating shuttle apparatus, instead of therotatable turret of FIGS. 2A-2D, which comprises a second apparatusembodiment. This second apparatus will now be described with respect toforming the preform of FIG. 5. FIG. 7 shows a time line of the sequenceof operations.

The apparatus (see FIGS. 6A-6D) includes first and second parallel guidebars 202, 203 on which a platen 205 is movably mounted in the directionof arrow A₄. The platen 205 carries a platform or shuttle 206 which ismovable in a transverse direction across the platen 205 as shown byarrow A₅. A fixed platen 212 at one end of the guide bars holds threeinjection mold cavity sets 213, 214 and 215 which are supplied bynozzles 218, 219 and 220 respectively. The left (first) and right(third) cavity sets 213 and 215 are used to form neck portions ofpreforms, while the middle (second) cavity set 214 is used for moldingbody-forming portions.

FIG. 5A shows an arbitrarily-designated first step wherein the firstcore set 207 is positioned in left cavity set 213 for forming a firstset of preform neck portions (sleeves). Simultaneously, second core set208 is positioned in middle cavity set 214 for molding a set ofmultilayer body-forming portions (over a second set of previously moldedneck portions). FIG. 5B shows the core sets following removal from thecavity sets, with a neck sleeve 250 on each core of core set 207, and apreform 260 on each core of core set 208. The completed preforms 260 arethen ejected from the core set 208.

In a second step (FIG. 6C), the shuttle 206 is moved to the right suchthat the first core set 207 with neck sleeves 250 are now positionedbelow middle cavity 214, while second core set 208 with now empty cores216 is positioned below right cavity set 215. Movable platen 205 is thenmoved towards fixed platen 212 so as to position first core set 207 inmiddle cavity set 214, and second core set 208 in right cavity set 215(FIG. 6D). Again, body-forming portions are formed over the previouslyformed neck sleeves in middle cavity set 214, while neck sleeves aremolded on each of the cores in the core set 208 in right cavity set 215.The movable platen 205 is then retracted to remove the core sets fromthe cavity sets, the finished preforms on the first core set 207 areejected, and the shuttle 206 returns to the left for molding the nextset of layers.

FIG. 7 is a time line of the operations shown in FIG. 6, with time inseconds along the x axis, and the sequence of steps in the second cavity214 shown above the x axis, and the sequence of steps in the firstcavity 213 shown below the x axis. First, at t=0, the mold is closed(FIG. 6A) and the pressure builds up. Then, at t=1.5 seconds, the secondcavity 214 is filled (forming the outer layer), the pressure increased,and the pressure held while the preform cools, until t=21 seconds.Meanwhile, no action is required in the first cavity at t=1.5 seconds;at t=20 seconds, the first cavity 213 is filled with PEN polymer and thepressure increased and held until t=21 seconds (again the hold andcooling stage has been substantially eliminated in the first cavity setby delaying the filling stage until near the end of the hold and coolingstage for the second cavity set). At t=21 seconds, the mold is openedand the preforms 260 are ejected from the second cavities. At t=23seconds, the shuttle 206 with the still warm neck sleeves is transferredto the second shuttle position as shown in FIG. 6C, and at t=24 secondsthe mold is closed as shown in FIG. 6D.

In this particular embodiment, the first and second core sets 207, 208are held at a temperature on the order of 60-70° C. during both of thefirst and second molding steps. The first mold cavity (for forming theneck finish sleeve) is on the order of 75-85° C. The PEN polymer has amelt temperature on the order of 275-285° C. The cycle time in the firstcavity is on the order of 5-6 seconds; this is the time lapse betweenthe first and second injection steps. The surface temperature of thesleeve at the time of the second injection is on the order of 100-110°C.

In the second molding step, the core temperature is on the order of60-70° C., and the second mold cavity is at a temperature on the orderof 5-10° C. The cycle time in the second mold cavity is on the order of23-25 seconds. The elevated temperature at the outer surface of thesleeve, at the time of the second molding step, causes melt adhesion(including diffusion bonding and chain entanglement) between the PENpolymer of the sleeve and the virgin PET of the outer layer portion 258which is adjacent the sleeve 250.

Third Preform Embodiment (Hot Fill)

A further preform/container embodiment is illustrated in FIGS. 8-9.FIGS. 8A-8B show a multilayer preform 330 and FIGS. 9A-9B show ahot-fill beverage bottle 370 made from the preform of FIG. 8. In thisembodiment, a first molded sleeve forms the entire thickness of the neckfinish, and is joined at its lower end to a second molded body-formingportion.

FIG. 8A shows a substantially cylindrical preform 330 (defined byvertical centerline 332) which includes an upper neck portion or finishsleeve 340 bonded to a lower body-forming portion 350. The crystallizedneck portion is a monolayer of CPET and includes an upper sealingsurface 341 which defines the open top end 342 of the preform, and anexterior surface having threads 343 and a lowermost flange 344. CPET,sold by Eastman Chemical, Kingsport, Tenn., is a polyethyleneterephthalate polymer with nucleating agents which cause the polymer tocrystallize during the injection molding process. Below the neck finish340 is a body-forming portion 350 which includes a flaredshoulder-forming section 351, increasing (radially inwardly) in wallthickness from top to bottom, a cylindrical panel-forming section 352having a substantially uniform wall thickness, and a base-formingsection 353. Body-forming section 350 is substantially amorphous and ismade of the following three layers in serial order: outer layer 354 ofvirgin PET; core layer 356 of post-consumer PET; and inner layer 358 ofvirgin PET. The virgin PET is a low copolymer having 3% comonomers(e.g., cyclohexane dimethanol (CHDM) or isophthalic acid (IPA)) by totalweight of the copolymer. A last shot of virgin PET (to clean the nozzle)forms a core layer 359 in the base.

This particular preform is designed for making a hot-fill beveragecontainer. In this embodiment, the preform has a height of about 96.3mm, and an outer diameter in the panel-forming section 352 of about 26.7mm. The total wall thickness at the panel-forming section 352 is about 4mm, and the thicknesses of the various layers are: outer layer 354 ofabout 1 mm, core layer 356 of about 2 mm, and inner layer 358 of about 1mm. The panel-forming section 352 may be stretched at an average planarstretch ratio of about 10:1, as described hereinafter. The planarstretch ratio is the ratio of the average thickness of the preformpanel-forming portion 352 to the average thickness of the containerpanel 383, wherein the “average” is taken along the length of therespective preform or container portion. For hot-fill beverage bottlesof about 0.5 to 2.0 liters in volume and about 0.35 to 0.60 millimetersin panel wall thickness, a preferred planar stretch ratio is about 9 to12, and more preferably about 10 to 11. The hoop stretch is preferablyabout 3.3 to 3.8 and the axial stretch about 2.8 to 3.2. This produces acontainer panel with the desired abuse resistance, and a preformsidewall with the desired visual transparency. The specific panelthickness and stretch ratio selected depend on the dimensions of thebottle, the internal pressure, and the processing characteristics (asdetermined for example, by the intrinsic viscosity of the particularmaterials employed).

In order to enhance the crystallinity of the neck portion, a highinjection mold temperature is used at the first molding station. In thisembodiment, CPET resin at a melt temperature of about 280 to 290° C. isinjection molded at a mold cavity temperature of about 110 to 120° C.and a core temperature of about 5 to 15° C., and a cycle time of about 6to 7 seconds. The first core set, carrying the still warm neck portions(outer surface temperature of about 115 to 125° C.), are thentransferred to the second station where multiple second polymers areinjected to form the multilayer body-forming portions and melt adhesionoccurs between the neck and body-forming portions. The core and/orcavity set at the second station are cooled (e.g., 5 to 15° C.core/cavity temperature) in order to solidify the performs and enableremoval from the molds (cycle time of about 23 to 25 seconds) withacceptable levels of post-mold shrinkage. The cores and cavities at boththe first and second stations include water cooling/heating passages foradjusting the temperature as desired.

As used herein, “melt adhesion” between the inner sleeve and outer layeris meant to include various types of bonding which occur due to theenhanced temperature (at the outer surface of the inner sleeve) andpressure (e.g., typical injection molding on the order of 8,000-15,000psi) during the second molding step, which may include diffusion,chemical, chain entanglement, hydrogen bonding, etc. Generally,diffusion and/or chain entanglement will be present to form a bond whichprevents delamination of the layers in the preform, and in the containerwhen filled with water at room temperature (25° C.) and dropped from aheight of eighteen inches onto a thick steel plate.

FIG. 8B is an expanded view of the neck finish 340 of preform 330. Themonolayer CPET neck finish is formed with a projection 345 at its lowerend, which is later surrounded (interlocked) by the virgin PET melt fromthe inner and outer layers 354,358 at the second molding station. TheCPET neck finish and outermost virgin PET layers of the body are meltadhered together in this intermediate region (between the lower end ofthe neck finish sleeve and the upper end of the body-forming region).

FIG. 9A shows a unitary expanded plastic preform container 370, madefrom the preform of FIG. 8. The container is about 182.0 mm in heightand about 71.4 mm in (widest) diameter. This 16-oz. container isintended for use as a hot-fill non-carbonated juice container. Thecontainer has an open top end with the same crystallized neck finish 340as the preform, with external screw threads 343 for receiving a screw-oncap (not shown). Below the neck finish 340 is a substantially amorphousand transparent expanded body portion 380. The body includes asubstantially vertically-disposed sidewall 381 (defined by verticalcenterline 372 of the bottle) and base 386. The sidewall includes anupper flared shoulder portion 382 increasing in diameter to asubstantially cylindrical panel portion 383. The panel 383 has aplurality of vertically-elongated, symmetrically-disposed vacuum panels385. The vacuum panels move inwardly to alleviate the vacuum formedduring product cooling in the sealed container, and thus preventpermanent, uncontrolled deformation of the container. The base 386 is achampagne-style base having a recessed central gate portion 387 andmoving radially outwardly toward the sidewall, an outwardly concave dome388, an inwardly concave chime 389, and a radially increasing andarcuate outer base portion 390 for a smooth transition to the sidewall381.

FIG. 9B shows in cross section the multilayer panel portion 383including an outer layer 392, a core layer 394, and an inner layer 396,corresponding to the outer 354, core 356 and inner 358 layers of thepreform. The inner and outer container layers 392, 396 (of virgin PETcopolymer) are each about 0.1 mm thick, and the core layer 394 (ofpost-consumer PET) is about 0.2 mm thick. The shoulder 382 and base 386are stretched less and therefore are relatively thicker and lessoriented than the panel 383.

Fourth Preform Embodiment

A fourth preform embodiment is illustrated in FIG. 10. A multilayerpreform 130 is made from the method and apparatus of FIGS. 1-2, and isadapted to be reheat stretch blow-molded into a refillable carbonatedbeverage bottle similar to that shown in FIG. 4, but having a thickenedbase area including the chime for increased resistance to caustic andpressure induced stress cracking.

In FIG. 10 there is shown a preform 130 which includes a PEN innersleeve layer 120, and a three-layer outer layer comprising outermost(exterior) virgin PET layer 123, first intermediate (interior) PC-PETlayer 124, and second intermediate (interior) virgin PET layer 125. Theinner sleeve layer 120 is continuous, having a body portion 121extending the full length of the preform and throughout the base. Thesleeve layer further includes an upper flange 122 which forms the topsealing surface of the preform. The outer layer similarly extends thefull length and throughout the bottom of the preform.

The preform 130 includes an upper neck finish 132, a flaredshoulder-forming section 134 which increases in thickness from top tobottom, a panel-forming section 136 having a uniform wall thickness, anda thickened base-forming section 138. Base section 138 includes an uppercylindrical thickened portion 133 (of greater thickness than the panelsection 136) which forms a thickened chime in the container base, and atapering lower portion 135 of reduced thickness for forming a recesseddome in the container base. A last shot of virgin PET (to clean thenozzle) forms a core layer 139 in the base. A preform having a preferredcross-section for refill applications is described in U.S. Pat. No.5,066,528 granted Nov. 19, 1991 to Krishnakumar et al., which is herebyincorporated by reference in its entirety.

This particular preform is designed for making a refillable carbonatedbeverage container. The use of an inner sleeve 120 of a PEN homopolymer,copolymer, or blend provides reduced flavor absorption and increasedthermal stability for increasing the wash temperature. The inner PENsleeve can be made relatively thin according to the method of FIG. 1.The interior PC-PET layer 124 can be made relatively thick to reduce thecost of the container, without significantly affecting performance. Inthis example, the preform has a height of about 7.130 inches (181.1 mm),and an outer diameter in the panel-forming section 136 of about 1.260inches (32.0 mm). At the panel-forming section 136, the total wallthickness is about 0.230 inches (5.84 mm), and the thicknesses of thevarious layers are: inner layer 120 of about 0.040 inches (1.0 mm),outermost layer 123 of about 0.040 inches (1.0 mm), first intermediatelayer 124 of about 0.130 inches (3.30 mm), and second intermediate layer125 of about 0.020 inches (0.5 mm). The panel-forming section 136 may bestretched at an average planar stretch ratio of about 10.5:1, asdescribed hereinafter. The planar stretch ratio is the ratio of theaverage thickness of the preform panel-forming portion 136 to theaverage thickness of the container panel (see for example sidewall 46 inFIG. 4), wherein the “average” is taken along the length of therespective preform or container portion. For refillable carbonatedbeverage bottles of about 0.5 to 2.0 liters in volume and about 0.5 to0.8 millimeters in panel wall thickness, a preferred planar stretchratio is about 7.5-10.5, and more preferably about 9.0-10.5. The hoopstretch is preferably about 3.2-3.5 and the axial stretch about 2.3-2.9.This produces a container panel with the desired abuse resistance, and apreform sidewall with the desired visual transparency. The specificpanel thickness and stretch ratio selected depend on the dimensions ofthe bottle, the internal pressure (e.g., 2 atmospheres for beer and 4atmospheres for soft drinks), and the processing characteristics (asdetermined for example, by the intrinsic viscosity of the particularmaterials employed).

In order to provide a thin PEN sleeve layer (e.g. 0.5 to 1.0 mm), asuitable mold cavity temperature would be on the order of 100 to 110° C.and core temperature of about 5 to 15° C., for a PET melt temperature ofabout 285 to 295° C. and cycle time of about 6 to 7 seconds. The firstcore set and warm inner layer are then immediately transferred to thesecond station where the outer layers are injected and bonding occursbetween the inner and outer layers (e.g., exterior surface of inner PENsleeve layer at about 90 to 100° C. and innermost PET layer at about 260to 275° C.). The first core set and/or second cavity set at the secondstation are cooled (e.g., about 5 to 15° C.) in order to solidify theperform and enable removal from the mold. The cores and cavities at boththe first and second stations include water cooling/heating passages foradjusting the temperature as desired.

In this embodiment, the inner sleeve layer 120 is made from a high-PENcopolymer having 90% PEN/10% PET by total weight of the layer, and inthe container panel is about 0.004 inches (0.10 mm) thick. The outermostlayer 123 is a virgin PET low copolymer having 3% comonomers (e.g., CHDMor IPA), and in the container panel is about 0.004 in (0.10 mm) thick.The first intermediate layer 124 is PC-PET, and in the container panelis about 0.012 in (0.30 mm) thick. The second intermediate layer 125 isthe same virgin PET low copolymer as outermost layer 123, and in thecontainer panel is about 0.002 in (0.05 mm) thick. The containershoulder and base (see 44 and 48 in FIG. 4A) are stretched less andtherefore are thicker and less oriented than the panel (see 46 in FIG.4A).

Fifth Preform Embodiment

FIG. 11 illustrates another preform embodiment for making a refillablecarbonated beverage container. This preform has an additional outermostlayer in the base only for increasing caustic stress crack resistance,while maximizing the use of post-consumer PET for reducing the cost. Thepreform 160 includes an upper neck finish 162, shoulder-forming portion164, panel-forming section 166, and base-forming portion 168. The innerlayer 170 has a body portion 171 which is continuous throughout thelength (including the bottom) of the preform and includes an upperflange 172 forming the top sealing surface. The inner layer is virginPET. An outer layer 173 of PC-PET extends throughout the length of thepreform, and forms a single outer layer in the neck finish andpanel-forming section. In the base-forming portion an additionalexterior layer 174 of high IV virgin PET is provided to enhance thecaustic stress crack resistance of the blown container. A thin interiorlayer 175 of the high IV virgin PET may also be formed according to thesequential injection process previously referenced. A last shot 176 ofhigh IV virgin PET is used to clear out the PC-PET from the nozzlesection. The outer base layer 174 is preferably a high IV virgin PET(homopolymer or copolymer) having an intrinsic viscosity of at leastabout 0.76, and preferably in the range of 0.76 to 0.84. The resultingcontainer may be either a footed or champagne base container.

Sixth Preform Embodiment

FIG. 12 shows another preform embodiment including a high-temperatureneck finish sleeve 190 and a single outer layer 194 for forming ahot-fill container. The preform 180 includes a neck finish 182,shoulder-forming portion 184, panel-forming portion 186, andbase-forming portion 188. The inner sleeve 190 includes a neck finishportion 191, extending substantially along the length of the upperthreaded neck finish portion 182 of the container, and an upper flange192 forming a top sealing surface. The inner sleeve is formed of athermal resistant (high T_(g)) material such as a PEN homopolymer,copolymer or blend. Alternatively, the sleeve may be formed of CPET,sold by Eastman Chemical, Kingsport, Tenn., a polyethylene terephthalatepolymer with nucleating agents which cause the polymer to crystallizeduring the injection molding process.

The outer layer 194 is made of virgin PET. This preform is intended formaking hot-fill containers, wherein the inner sleeve 190 providesadditional thermal stability at the neck finish.

In further alternative embodiments, a triple outer layer of virgin PET,PC-PET, and virgin PET may be used.

Alternative Constructions and Materials

There are numerous preform and container constructions, and manydifferent injection moldable materials, which may be adapted for aparticular food product and/or package, filling, and manufacturingprocess. Additional representative examples are given below.

Thermoplastic polymers useful in the present invention includepolyesters, polyamides and polycarbonates. Suitable polyesters includehomopolymers, copolymers or blends of polyethylene terephthalate (PET),polybutylene terephthalate (PBT), polypropylene terephthalate (PPT),polyethylene napthalate (PEN), and a cyclohexane dimethanol/PETcopolymer, known as PETG (available from Eastman Chemical, Kingsport,Tenn.). Suitable polyamides (PA) include PA6, PA6,6, PA6,4, PA6,10,PA11, PA12, etc. Other useful thermoplastic polymers includeacrylic/imide, amorphous nylon, polyacrylonitrile (PAN), polystyrene,crystallizable nylon (MXD-6), polyethylene (PE), polypropylene (PP), andpolyvinyl chloride (PVC).

Polyesters based on terephthalic or isophthalic acid are commerciallyavailable and convenient. The hydroxy compounds are typically ethyleneglycol and 1,4-di-(hydroxy methyl)-cyclohexane. The intrinsic viscosityfor phthalate polyesters are typically in the range of 0.6 to 1.2, andmore particularly 0.7 to 1.0 (for O-chlorolphenol solvent). 0.6corresponds approximately to a viscosity average molecular weight of59,000, and 1.2 to a viscosity average molecular weight of 112,000. Ingeneral, the phthalate polyester may include polymer linkages, sidechains, and end groups not related to the formal precursors of a simplephthalate polyester previously specified. Conveniently, at least 90 molepercent will be terephthalic acid and at least 90 mole percent analiphatic glycol or glycols, especially ethylene glycol.

Post-consumer PET (PC-PET) is a type of recycled PET prepared from PETplastic containers and other recyclables that are returned by consumersfor a recycling operation, and has now been approved by the FDA for usein certain food containers. PC-PET is known to have a certain level ofI.V. (intrinsic viscosity), moisture content, and contaminants. Forexample, typical PC-PET (having a flake size of one-half inch maximum),has an I.V. average of about 0.66 dl/g, a relative humidity of less than0.25%, and the following levels of contaminants:

PVC: <100 ppm

aluminum: <50 ppm

olefin polymers (HDPE, LDPE, PP): <500 ppm

paper and labels: <250 ppm

colored PET: <2000 ppm

other contaminants: <500 ppm

PC-PET may be used alone or in one or more layers for reducing the costor for other benefits.

Also useful as a base polymer or as a thermal resistant and/orhigh-oxygen barrier layer is a packaging material with physicalproperties similar to PET, namely polyethylene naphthalate (PEN). PENprovides a 3-5× improvement in barrier property and enhanced thermalresistance, at some additional expense. Polyethylene naphthalate (PEN)is a polyester produced when dimethyl 2,6-naphthalene dicarboxylate(NDC) is reacted with ethylene glycol. The PEN polymer comprisesrepeating units of ethylene 2,6 naphthalate. PEN resin is availablehaving an inherent viscosity of 0.67 dl/g and a molecular weight ofabout 20,000 from Amoco Chemical Company, Chicago, Ill. PEN has a glasstransition temperature T_(g) of about 123° C., and a melting temperatureT_(m) of about 267° C.

Oxygen barrier layers include ethylene/vinyl alcohol (EVOH), PEN,polyvinyl alcohol (PVOH), polyvinyldene chloride (PVDC), nylon 6,crystallizable nylon (MXD-6), LCP (liquid crystal polymer), amorphousnylon, polyacrylonitrile (PAN) and styrene acrylonitrile (SAN).

The intrinsic viscosity (I.V.) effects the processability of the resins.Polyethylene terephthalate having an intrinsic viscosity of about 0.8 iswidely used in the carbonated soft drink (CSD) industry. Polyesterresins for various applications may range from about 0.55 to about 1.04,and more particularly from about 0.65 to 0.85 dl/g. Intrinsic viscositymeasurements of polyester resins are made according to the procedure ofASTM D-2857, by employing 0.0050±0.0002 g/ml of the polymer in a solventcomprising o-chlorophenol (melting point 0° C.), respectively, at 30° C.Intrinsic viscosity (I.V.) is given by the following formula:

I.V.=(ln(V _(Soln.) /V _(Sol.)))/C

where:

V_(Soln.) is the viscosity of the solution in any units;

V_(Sol.) is the viscosity of the solvent in the same units; and

C is the concentration in grams of polymer per 100 mls of solution.

The blown container body should be substantially transparent. Onemeasure of transparency is the percent haze for transmitted lightthrough the wall (H_(T)) which is given by the following formula:

H _(T) =[Y _(d)÷(Y _(d) +Y _(s))]×100

where Y_(d) is the diffuse light transmitted by the specimen, and Y_(s)is the specular light transmitted by the specimen. The diffuse andspecular light transmission values are measured in accordance with ASTMMethod D 1003, using any standard color difference meter such as modelD25D3P manufactured by Hunterlab, Inc. The container body should have apercent haze (through the panel wall) of less than about 10%, and morepreferably less than about 5%.

The preform body-forming portion should also be substantially amorphousand transparent, having a percent haze across the wall of no more thanabout 10%, and more preferably no more than about 5%.

The container will have varying levels of crystallinity at variouspositions along the height of the bottle from the neck finish to thebase. The percent crystallinity may be determined according to ASTM 1505as follows:

% crystallinity=[(ds−da)/(dc−da)]×100

where ds=sample density in g/cm³, da=density of an amorphous film ofzero percent crystallinity, and dc=density of the crystal calculatedfrom unit cell parameters. The panel portion of the container isstretched the greatest and preferably has an average percentcrystallinity in at least the outer layer of at least about 15%, andmore preferably at least about 20%. For primarily PET polymers, a 15-25%crystallinity range is useful in refill and hot-fill applications.

Further increases in crystallinity can be achieved by heat setting toprovide a combination of strain-induced and thermal-inducedcrystallization. Thermal-induced crystallinity is achieved at lowtemperatures to preserve transparency, e.g., holding the container incontact with a low temperature blow mold. In some applications, a highlevel of crystallinity at the surface of the sidewall alone issufficient.

As a further alternative embodiment, the preform may include one or morelayers of an oxygen scavenging material. Suitable oxygen scavengingmaterials are described in U.S. Ser. No. 08/355,703 filed Dec. 14, 1994by Collette et al., entitled “Oxygen Scavenging Composition ForMultilayer Preform And Container,” which is hereby incorporated byreference in its entirety. As disclosed therein, the oxygen scavengermay be a metal-catalyzed oxidizable organic polymer, such as apolyamide, or an anti-oxidant such as phosphite or phenolic. The oxygenscavenger may be mixed with PC-PET to accelerate activation of thescavenger. The oxygen scavenger may be advantageously combined withother thermoplastic polymers to provide the desired injection moldingand stretch blow molding characteristics for making substantiallyamorphous injection molded preforms and substantially transparentbiaxially oriented polyester containers. The oxygen scavenger may beprovided as an interior layer to retard migration of the oxygenscavenger or its byproducts, and to prevent premature activation of thescavenger.

Refillable containers must fulfill several key performance criteria inorder to achieve commercial viability, including:

1. high clarity (transparency) to permit visual on-line inspection;

2. dimensional stability over the life of the container; and

3. resistance to caustic wash induced stress cracking and leakage.

Generally, a refillable plastic bottle must maintain its functional andaesthetic characteristics over a minimum of 10 and preferably 20 cyclesor loops to be economically feasible. A cycle is generally comprised of(1) an empty hot caustic wash, (2) contaminant inspection (before and/orafter wash) and product filling/capping, (3) warehouse storage, (4)distribution to wholesale and retail locations and (5) purchase, use andempty storage by the consumer, followed by eventual return to thebottler.

A test procedure for simulating such a cycle would be as follows. Asused in this specification and claims, the ability to withstand adesignated number of refill cycles without crack failure and/or with amaximum volume change is determined according to the following testprocedure.

Each container is subjected to a typical commercial caustic washsolution prepared with 3.5% sodium hydroxide by weight and tap water.The wash solution is maintained at a designated wash temperature, e.g.,60° C. The bottles are submerged uncapped in the wash for 15 minutes tosimulate the time/temperature conditions of a commercial bottle washsystem. After removal from the wash solution, the bottles are rinsed intap water and then filled with a carbonated water solution at 4.0±0.2atmospheres (to simulate the pressure in a carbonated soft drinkcontainer), capped and placed in a 38° C. convection oven at 50%relative humidity for 24 hours. This elevated oven temperature isselected to simulate longer commercial storage periods at lower ambienttemperatures. Upon removal from the oven, the containers are emptied andagain subjected to the same refill cycle, until failure.

A failure is defined as any crack propagating through the bottle wallwhich results in leakage and pressure loss. Volume change is determinedby comparing the volume of liquid the container will hold at roomtemperature, both before and after each refill cycle.

A refillable container can preferably withstand at least 20 refillcycles at a wash temperature of 60° C. without failure, and with no morethan 1.5% volume change after 20 cycles.

In this invention, a higher level of crystallization can be achieved inthe neck finish compared to prior art processes which crystallizeoutside the mold. Thus, the preform neck finish may have a level ofcrystallinity of at least about 30%. As a further example, a neck finishmade of a PET homopolymer can be molded with an average percentcrystallinity of at least about 35%, and more preferably at least about40% To facilitate bonding between the neck portion and body-formingportion of the preform, one may use a thread split cavity, wherein thethread section of the mold is at a temperature above 60° C., andpreferably above 75° C.

As an additional benefit, a colored neck finish can be produced, whilemaintaining a transparent container body.

The neck portion can be monolayer or multilayer and made of variouspolymers other than CPET, such as arylate polymers, polyethylenenaphthalate (PEN), polycarbonates, polypropylene, polyimides,polysulfones, acrylonitrile styrene, etc. As a further alternative, theneck portion can be made of a regular bottle-grade homopolymer or lowcopolymer PET (i.e., having a low crystallization rate), but thetemperature or other conditions of the first molding station can beadjusted to crystallize the neck portion.

Other benefits include the achievement of higher hot-fill temperatures(i.e., above 85° C.) because of the increased thermal resistance of thefinish, and higher refill wash temperatures (i.e., above 60° C.). Theincreased thermal resistance is also particularly useful inpasteurizable containers.

FIGS. 13A-13B illustrate graphically the change in melt temperature andorientation temperature for PET/PEN compositions, as the weight percentof PEN increases from 0 to 100. There are three classes of PET/PENcopolymers or blends: (a) a high-PEN concentration having on the orderof 80-100% PEN and 0-20% PET by total weight of the copolymer or blend,which is a strain-hardenable (orientable) and crystallizable material;(b) a mid-PEN. concentration having on the order of 20-80% PEN and80-20% PET, which is an amorphous non-crystallizable material that willnot undergo strain hardening; and (c) a low-PEN concentration having onthe order of 1-20% PEN and 80-99% PET, which is a crystallizable andstrain-hardenable material. A particular PEN/PET polymer or blend can beselected from FIGS. 13A-13B based on the particular application.

FIG. 14 illustrates a particular embodiment of a combined infrared (IR)and radio frequency (RF) heating system for reheating previously moldedand cooled preforms (i.e., for use in a two-stage reheat injection moldand stretch blow process). This system is intended for reheatingpreforms having layers with substantially different orientationtemperatures. For example, in the fourth preform embodiment the high-PENinner layer 120 has an orientation temperature much higher than thevirgin PET low copolymer and PC-PET outer layers 123-125. PENhomopolymer has a minimum orientation temperature on the order of 260°F. (127° C.), based on a glass transition temperature on the order of255° F. (123° C.). PEN homopolymer has a preferred orientation range ofabout 270-295° F. (132-146° C.). In contrast, PET homopolymer has aglass transition temperature on the order of 175° F. (80° C.). At theminimum orientation temperature of PEN homopolymer, PET homopolymerwould begin to crystallize and would no longer undergo strain hardening(orientation), and the resulting container would be opaque and haveinsufficient strength.

Returning to FIG. 14, this combined reheating apparatus may be used withpreforms having a substantial disparity in orientation temperaturesbetween layers. The preforms 130 are held at the upper neck finish by acollet 107 and travel along an endless chain 115 through stations A, Band C in serial order. Station A is a radiant heating oven in which thepreforms are rotated while passing by a series of quartz heaters. Theheating of each preform is primarily from the exterior surface and heatis transmitted across the wall to the inner layer. The resulting heat ortemperature profile is higher at the exterior surface of the preformthan at the interior surface. The time and temperature may be adjustedin an attempt to equilibriate the temperature across the wall.

In this embodiment, it is desired to heat the inner PEN layer at ahigher temperature because of PEN's higher orientation temperature.Thus, the preforms (across the wall) are brought up to an initialtemperature of about 160° F. (71° C.) at station A, and are thentransferred to station B which utilizes microwave or radio frequencyheaters. These high-frequency dielectric heaters provide a reversetemperature profile from that of the quartz heaters, with the interiorsurface of the preform being heated to a higher temperature than that ofthe exterior surface. FIG. 14 shows the preforms 130 traveling betweenelectrode plates 108 and 109, which are connected to RF generator 110and ground respectively. At station B, the inner layer is brought up toa temperature of about 295° F. (146° C.), and the outer layer to atemperature of about 200° F. (93° C.). Finally, the preforms are passedto station C, which is similar to station A. At station C the quartzheaters bring the preforms to a temperature of about 280° F. (138° C.)at the inner layer and about 210° F. (99° C.) at the outer layer. Thereheated preforms are then sent to a blow mold for stretch blow molding.A more detailed description of hybrid reheating of polyester preformsincluding a combination of quartz oven reheating and radio frequencyreheating is described in U.S. Pat. No. 4,731,513 to Collette entitled“Method Of Reheating Preforms For Forming Blow Molded Hot FillableContainers,” which issued Mar. 15, 1988, and is hereby incorporated byreference. In addition, additives may be provided in either or both ofthe PET and PEN layers to make them more receptive to radio frequencyheating.

In a preferred thin sleeve/thick outer layer embodiment, the thin innerlayer sleeve may have a thickness on the order of 0.02 to 0.06 inch (0.5to 1.5 mm), while the thick outer layer has a wall thickness on theorder of 0.10 to 0.25 inch (2.50 to 6.35 mm). The inner layer maycomprise on the order of 10-20% by total weight of the preform. Thisrepresents an improvement over the prior art single injection cavityprocess for making multilayer preforms. Also, the weight of one or moreouter layers (such as a layer of PC-PET) can be maximized.

While there have been shown and described several embodiments of thepresent invention, it will be obvious to those skilled in the art thatvarious changes and modifications may be made therein without departingfrom the scope of the invention as defined by the appending claims.

What is claimed is:
 1. A method of making a multilayer injection-moldedplastic article, the method comprising: firstly molding an inner sleevelayer between a first mold cavity and core, the first mold cavity beingheated in order to provide an outer surface of the inner sleeve layer atan elevated temperature in a subsequent molding step; transferring thecore and sleeve layer to a second mold cavity and secondly molding anouter layer over the sleeve layer while the outer surface is at theelevated temperature, the outer layer having a thickness greater thanthe thickness of the inner sleeve layer, where the elevated temperatureis selected to provide melt adhesion between the inner sleeve and theouter layer during the second molding step.
 2. The method of claim 1,wherein: the inner sleeve comprises a nonrecycled polymer; and the outerlayer comprises a recycled polymer.
 3. The method of claim 2, wherein:the nonrecycled polymer is a virgin polyethylene terephthalate (PET)polymer including homopolymer, low copolymer and blends of PET; and therecycled polymer is recycled PET.
 4. The method of claim 3, wherein: theinner sleeve comprises up to 20% by weight of the article.
 5. The methodof claim 4, wherein: the inner sleeve comprises on the order of 10% byweight of the article.
 6. The method of claim 3, wherein: the innersleeve is a full-length Inner sleeve of nonrecycled PET comprising up to20% by weight of the article; the outer layer includes at least onelayer of recycled PET.
 7. The method of claim 1, wherein the innersleeve is selected from the group consisting of: a full-length sleeveportion; an upper sleeve portion; a full-thickness upper sleeve portion;and a sleeve portion including an upper surface of the article; and theinner sleeve comprises a polymer selected from the group consisting of:a high T_(g) polymer; a polyethylene naphthalate (PEN) polymer includinghomopolymer, low copolymer and blends of PEN; and a crystallizablepolymer.
 8. The method of claim 1, wherein: the article is a preform formaking a beverage container.
 9. The method of claim 8, wherein: thearticle is expanded to make a beverage container selected from the groupconsisting of carbonated beverage, hot-fillable, refillable,pasteurizable, and oxygen-barrier containers.
 10. The method of claim 1,wherein the melt adhesion between the inner sleeve and outer layerincludes one or more of diffusion bonding and chain entanglement. 11.The method of claim 1, wherein the sleeve forms an upper sleeve portionof the article, and the outer layer forms a lower body portion of thearticle.
 12. The method of claim 11, wherein the upper sleeve portion iscrystallized in the first mold cavity.
 13. The method of claim 1,wherein the first molding step forms the inner sleeve as: a full-lengthsleeve portion; an upper sleeve portion; a full-thickness upper sleeveportion; and a sleeve portion including an upper surface of the article.14. The method of claim 1, wherein the outer layer comprises multipleouter layers.
 15. The method of claim 1, wherein the article is apreform.
 16. The method of claim 15, wherein the first molding stepforms a neck finish portion of the preform.
 17. The method of claim 16,wherein the neck finish portion is molded from a polymer whichcrystallizes during the first molding step.
 18. The method of claim 16,wherein the neck finish portion is molded from a first polymer materialhaving a higher glass transition temperature than a second polymermaterial which forms the outer layer.
 19. The method of claim 1, whereinthe sleeve is crystallized during the first molding step.
 20. The methodof claim 1, wherein the sleeve has a wall thickness in a range on theorder of 0.5 to 1.5 mm.
 21. The method of claim 20, wherein the outerlayer has a wall thickness in a range on the order of 2.50 to 6.35 mm.22. The method of claim 1, wherein the inner sleeve is formed of a firstmaterial having a first melt temperature, and the outer layer includes asecond layer adjacent the inner sleeve and made of a second materialhaving a second melt temperature lower than the first melt temperature.23. The method of claim 22, wherein: the inner sleeve comprises a firstpolyethylene terephthalate (PET) polymer; and the outer layer comprisesa second PET polymer.
 24. The method of claim 23, wherein: each of thefirst and second PET polymers are selected from the group consisting ofPET homopolymer and low copolymers.
 25. The method of claim 24, wherein:the first PET polymer has an intrinsic viscosity of at least 0.76. 26.The method of claim 25, wherein: the inner sleeve has a wall thicknessin a range of 0.5 to 1.5 mm; and the outer layer has a wall thickness inrange of 2.50 to 6.35 mm.
 27. The method of claim 23, wherein: thearticle is a preform for making a beverage container.
 28. The method ofclaim 27, wherein: the preform has a body portion and the method furthercomprises expanding the body portion of the preform to form a containerhaving a substantially transparent and biaxially-oriented body portion.29. The method of claim 1, wherein the first mold cavity is at a firstcavity temperature and the second mold cavity is at a second cavitytemperature lower than the first cavity temperature.
 30. The method ofclaim 29, wherein the core is at a core temperature which is less thanthe first cavity temperature.
 31. The method of claim 1, wherein theinner sleeve is formed of a first material having a first T_(g), and theelevated temperature is in a range on the order of 5-20° below the firstT_(g).
 32. The method of claim 1, wherein the sleeve is molded from afirst material selected from the group consisting of homopolymers,copolymers, and blends of polyethylene naphthalate (PEN).
 33. The methodof claim 1, wherein the outer layer includes at least one layer moldedfrom a second material selected from the group consisting ofpolyethylene terephthalate (PET), recycled PET, polyethylene,polypropylene, polyacrylate, polycarbonate, polyacrylonitrile, nylon,and copolymers and blends thereof.
 34. The method of claim 1, whereinthe article has a sidewall portion in which the Inner sleeve has a firstthickness (t₁) and the outer layer has a second thickness (t₂), and theratio of t₂:t₁ is greater than on the order of 4:1.
 35. The method ofclaim 1, wherein the inner sleeve has a first thickness (t₁) and theouter layer has a second thickness (t₂), and the ratio of t₂:t₁ is onthe order of from 1.2:1 to 8:1.
 36. The method of claim 1, wherein theinner sleeve is substantially crystallized and the outer layer issubstantially amorphous.
 37. The method of claim 1, wherein the innersleeve is made of a first material and the outer layer is made of asecond material, and the second material has a lower crystallizationrate compared to the first material.
 38. The method of claim 1, whereinfirst and second cores are provided, and wherein during a first cyclethe first core is positioned in the first mold cavity to form a firstinner sleeve, and the second core, having a second inner sleevepositioned thereon, is simultaneously positioned in the second moldcavity for molding a second outer layer on the second inner sleeve. 39.The method of claim 1, wherein the first molding step includes aninitial no-action period during which the second molding step proceedsin order to facilitate the second molding step with the outer surface ofthe sleeve layer at the elevated temperature.
 40. The method of claim 1,wherein the sleeve is molded of a first material selected from the groupconsisting of polyester, polyester with nucleating agents, acrylate,polyethylene naphthalate (PEN), polycarbonate, polypropylene, polyamide,polysulfone, acrylonitrile styrene, and copolymers and blends thereof.41. The method of claim 40, wherein the outer layer includes a secondmaterial selected from the group consisting of homopolymers, copolymers,and blends of any one or more of: polyethylene terephthalate (PET),polyethylene naphthalate (PEN), and recycled PET.
 42. The method ofclaim 1, wherein the article has a body portion and the method furthercomprises expanding the body portion of the article to form an expandedarticle having a substantially transparent and biaxially-oriented bodyportion.
 43. The method of claim 1, wherein the method further comprisescooling the article below a first glass transition temperature of afirst material comprising the inner sleeve layer, reheating the articleabove the first glass transition temperature, and expanding the reheatedarticle to form an expanded article.
 44. The method of claim 1, whereinthe expanded article has a high T_(g) or crystallized upper neck finishportion and a substantially transparent, biaxially-oriented bodyportion.
 45. A method of molding a multilayer plastic article in which afirst layer is molded over a core in a first mold cavity and the firstlayer and core are transferred to a second mold cavity where a secondlayer is molded, wherein: there is substantially eliminated any coolingstage in the first mold in order to provide an outer surface of thefirst layer at an elevated temperature in the second mold which enablesmelt adhesion between the outer surface of the first layer and thesecond layer.
 46. The method of claim 45, wherein there is provided aninitial no action period in the first mold, before a filling andpressure stage.
 47. The method of claim 45, wherein there is,simultaneous with molding of the first layer over a core in the firstmold, molding of a second layer over a previously molded first layer ona second core in the second mold.